This seems very, very complicated. I think capture-by-advance and capture-by-withdraw are worthy of "direct" support. I know we are running out of modifier letters. How about we take one of the remaining letters and use it exclusively as a prefix to give us 26 more? For example, if "x" is unused, x would be a prefix and we could say that xa is capture-by-advance and xw is capture-by-withdraw. And, if we should ever need even more, we could start using xx as a prefix.
This seems very, very complicated. I think capture-by-advance and capture-by-withdraw are worthy of "direct" support. I know we are running out of modifier letters. How about we take one of the remaining letters and use it exclusively as a prefix to give us 26 more? For example, if "x" is unused, x would be a prefix and we could say that xa is capture-by-advance and xw is capture-by-withdraw. And, if we should ever need even more, we could start using xx as a prefix.